1. Field of the Invention
The present invention relates to a method of expelling a fluid. More particularly, the present invention relates to a method of expelling a fluid from a nozzle using an ion wind and an ink-jet printhead utilizing the method.
2. Description of the Related Art
Typically, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of printing ink at a desired position on a recording sheet. In conventional ink-jet printheads, ink ejection mechanisms are largely categorized into two types. Conventionally, there have been used a thermally driven type in which a heat source is employed to generate bubbles in ink to cause ink droplets to be ejected by an expansion force of the generated bubbles, and a piezoelectrically driven type in which ink is ejected by a pressure applied to ink due to deformation of a piezoelectric element.
FIGS. 1A and 1B illustrate examples of a conventional thermally driven ink-jet printhead. FIG. 1A illustrates a cutaway perspective view of a structure of a conventional ink-jet printhead. FIG. 1B illustrates a cross-sectional view of an ink ejection mechanism of the conventional ink-jet printhead shown in FIG. 1A.
The conventional thermally driven ink-jet printhead shown in FIGS. 1A and 1B includes a manifold 22 provided on a substrate 10, an ink channel 24 and an ink chamber 26 defined by a barrier wall 14 installed on the substrate 10, a heater 12 installed in the ink chamber 26, and a nozzle 16 that is provided on a nozzle plate 18 and through which ink droplets 29′ are expelled. When a pulse current is supplied to the heater 12 and heat is generated in the heater 12, ink 29 filled in the ink chamber 26 is heated, and a bubble 28 is generated. The formed bubble 28 continuously expands and exerts pressure on the ink 29 contained within the ink chamber 26. This pressure causes the ink droplets 29′ to be expelled through the nozzle 16. Subsequently, the ink 29 is absorbed from the manifold 22 into the ink chamber 26 through the ink channel 24, thereby refilling the ink chamber 26 with ink 29.
However, in the thermally driven ink-jet printhead, when ink droplets are expelled due to the expansion of bubbles, a portion of the ink in the ink chamber 26 flows backward to the manifold 22, and an ink refill operation is performed after ink is expelled. Thus, there is a limitation in implementing high-speed printing.
In addition to the above-described ink droplet ejection mechanisms, a variety of different ink droplet ejection mechanisms are used in ink-jet printheads, and another example is shown in FIG. 2. FIG. 2 illustrates an example of a conventional ink droplet ejection mechanism utilizing a principle of an atomizer.
Referring to FIG. 2, unmixed ink 40 of multiple colors is contained in a reservoir 34 of an ink cartridge 32. The reservoir 34 has a printhead 35 at a bottom surface thereof. The printhead 35 operates to dispense unmixed ink 40. The ink 40 dispensed through the printhead 35 is mixed in a mixing chamber 42, and a nozzle tube 44 is filled with the mixed ink. Compressed air delivered via a conduit 52 of an atomizer 50 is sprayed onto a front portion of an outlet 46 of the nozzle tube 44, causing a reduction in pressure at the front portion of the outlet 46 of the nozzle tube 44. Accordingly, ink in the nozzle tube 44 is expelled and atomized onto an object 49 in the form of droplets 48.
The ink-jet printhead expelling ink utilizing the principle of an atomizer requires a compressor for supplying compressed air. In particular, in order to adopt the above-described ink ejection mechanism to an ink-jet printhead having a plurality of nozzles, there is a demand for a complex series of air supply passages from the compressor to the plurality of nozzles. Thus, the printhead becomes bulky, which reduces the number of nozzles per unit area, i.e., a nozzle density. In addition, it is quite difficult to manufacture a printhead having several hundred or more nozzles. As a result, an operational printing resolution of the ink-jet printhead adopting the above-described ink ejection mechanism still remains at a level of several tens of dots per inch (DPI).
Accordingly, in order to implement an ink-jet printhead having high printing speed and high resolution, a new ink droplet ejection mechanism is needed.